By Dr. Mercola
People everywhere are finally waking up to the indisputable fact that all sugars are not created equal when it comes to the physical end results they create.
Scientists using newer functional magnetic resonance imaging (fMRI) tests have now shown that fructose, a sugar found in most processed foods (typically in the form of high fructose corn syrup), can in fact trigger changes in your brain that may lead to overeating and weight gain.1
The researchers discovered that when you drink a beverage containing fructose, your brain does not register the feeling of being satiated, as it does when you consume simple glucose. As reported by Yahoo! Health:2
“All sugars are not equal — even though they contain the same amount of calories — because they are metabolized differently in the body.
Table sugar is sucrose, which is half fructose, half glucose. High-fructose corn syrup is 55 percent fructose and 45 percent glucose. Some nutrition experts say this sweetener may pose special risks, but others and the industry reject that claim. And doctors say we eat too much sugar in all forms.”
Beware: Fructose Can Make You Hungry, Study Finds
Twenty healthy adults were included in the featured study, published in the journal JAMA on January 2.3 fMRI was used to measure the hypothalamus response when the volunteers consumed a beverage containing identical amounts of either fructose or glucose (75 grams). The two drinks were given in random order to all participants during testing sessions spaced eight months apart.
Your hypothalamus helps regulate hunger-related signals involving a number of hormones, including insulin, leptin, and ghrelin. The scans revealed that when drinking glucose, within 15 minutes the activity in the area of the brain involved with reward and desire for food was suppressed, which leads to a feeling of fullness or satiety. According to co-author Dr. Robert Sherwin:4
“With fructose, we don’t see those changes. As a result, the desire to eat continues — it isn’t turned off.”
In fact, fructose not only did not suppress hypothalamic activity, it actually caused a small spike instead. Furthermore, glucose boosted the links between the hypothalamus, thalamus, and striatum, while fructose strengthened the connectivity between the hypothalamus and thalamus, but not the striatum. This is important, as the striatum also deactivates once your body senses it has eaten enough… According to the authors:
“These findings suggest that ingestion of glucose, but not fructose, initiates a coordinated response between the homeostatic-striatal network that regulates feeding behavior.”
What all this means in everyday terms is that when you consume fructose, you may actually be “programming” your body to consume more calories, as fructose fails to trigger that feeling of fullness, and may even trigger continued hunger pangs. Dr. Jonathan Purnell, an endocrinologist at Oregon Health Science University, told Yahoo! Health:
“It implies that fructose, at least with regards to promoting food intake and weight gain, is a bad actor compared to glucose.”
How Your Body Metabolizes Fructose Versus Glucose
Part of what makes fructose so unhealthy is that it is metabolized by your liver to fat in far more rapidly than any other sugar. The entire burden of metabolizing fructose falls on your liver, and it promotes visceral fat.5 This is the type of fat that collects around your organs and in your abdominal region and is associated with a greater risk of heart disease.
Without getting into the complex biochemistry of carbohydrate metabolism, it is important to understand how your body processes fructose versus glucose. Dr. Robert Lustig, Professor of Pediatrics in the Division of Endocrinology at the University of California, has been a pioneer in decoding sugar metabolism. His work has highlighted some major differences in how different sugars are broken down and used. Here’s a summary of the main points:
- After eating fructose, 100 percent of the metabolic burden rests on your liver. With glucose, your liver has to break down only 20 percent. The metabolism of fructose by your liver creates a long list of waste products and toxins, including a large amount of uric acid, which drives up blood pressure and causes gout.
- Every cell in your body, including your brain, utilizes glucose. Therefore, much of it is “burned up” immediately after you consume it. By contrast, fructose is turned into free fatty acids (FFAs), VLDL (the damaging form of cholesterol), and triglycerides, which get stored as fat.
- The fatty acids created during fructose metabolism accumulate as fat droplets in your liver and skeletal muscle tissues, causing insulin resistance and non-alcoholic fatty liver disease (NAFLD).6 Insulin resistance progresses to metabolic syndrome and type II diabetes.
- Fructose is the most lipophilic carbohydrate. In other words, fructose converts to glycerol 3 phosphate (g-3-p), which is directly used to turn FFAs into triglycerides. The more g-3-p you have, the more fat you store. Glucose does not do this.
- When you eat 120 calories of glucose, less than one calorie is stored as fat. 120 calories of fructose results in 40 calories being stored as fat.
- Glucose suppresses your hunger hormone ghrelin and stimulates leptin, which suppresses your appetite. Fructose has no effect on ghrelin and interferes with your brain’s communication with leptin, resulting in overeating.
Known Health Ramifications of a High-Fructose Diet
Consuming foods that contain high amounts of fructose—even if it’s a natural product—is, to put it bluntly, the fastest way to trash your health. GreenMedInfo.com,7 has collated a number of scientific studies that have linked fructose to about 30 different specific diseases and health problems.
Adding insult to injury, HFCS is most often made from genetically engineered corn, which is fraught with its own well documented side effects and health concerns, from an increased risk of developing food allergies to the risk of increased infertility in future generations, and possibly cancer, according to a recent lifetime feeding study. Select the hyperlinks provided to review how fructose may:
Raise your blood pressure, and cause nocturnal hypertension
Promote insulin resistance / Type 2 Diabetes
Cause non-alcoholic fatty liver disease (NAFLD)
Raise your uric acid levels, which can result in gout and/or metabolic syndrome
Accelerate the progression of chronic kidney disease
Intracranial atherosclerosis (narrowing and hardening of the arteries in your skull)
Exacerbate cardiac abnormalities if you’re deficient in copper
Have a genotoxic effect on the colon
Promote metastasis in breast cancer patients
Cause tubulointerstitial injury (injury to the tubules and interstitial tissue of your kidney)
Promote obesity and related health problems and diseases
Promote pancreatic cancer growth and feed cancer cells in general
Cause your brain neurons to stagnate
Deplete vitamins and minerals (unbound fructose, found in large quantities in high fructose corn syrup, can interfere with your heart’s use of minerals such as magnesium, copper and chromium)
Promote arthritis and gout
My Recommended Fructose Allowance
With regards to the featured study findings, Scientific American notes:8
“Could fructose consumption alone really be playing such an outsized role in expanding our pant sizes? ‘A common counter argument is that it is the excess calories that are important, not the food. Simply put: just eat less,’ Purnell and Fair noted. ‘The reality, however, is that hunger and fullness are major determinants of how much humans eat, just as thirst determines how much humans drink.
These sensations cannot simply be willed away or ignored.’ In order to eat less (and consume fewer calories overall), they argued, then, one should avoid foods or ingredients that fail to satisfy hunger. And that, according to the results from the new study, would mean those fructose-sweetened foods—and drinks.”
As a standard recommendation, I advise keeping your TOTAL fructose consumption below 25 grams per day. For most people it would also be wise to limit your fructose from fruit to 15 grams or less, as you’re virtually guaranteed to consume “hidden” sources of fructose if you drink beverages other than water and eat processed food.
Fifteen grams of fructose is not much — it represents two bananas, one-third cup of raisins, or two Medjool dates. Remember, the average 12-ounce can of soda contains 40 grams of sugar, at least half of which is fructose, so one can of soda alone would exceed your daily allotment.
In his book, The Sugar Fix, Dr. Richard Johnson includes detailed tables showing the content of fructose in different foods — an information base that isn’t readily available when you’re trying to find out exactly how much fructose is in various foods. I encourage you to pick up a copy of this excellent resource. You can find an abbreviated listing of the fructose content of common fruits in this previous article.
How Fructose Affects Your “Fat Switch”
Dr. Johnson has also authored another book that is of major importance to anyone who has ever struggled with their weight and/or persistent health issues. According to Dr. Johnson, based on his decades of research:
“Those of us who are obese eat more because of a faulty ‘switch’ and exercise less because of a low energy state. If you can learn how to control the specific ‘switch’ located in the powerhouse of each of your cells – the mitochondria – you hold the key to fighting obesity.”
There are five basic truths that Dr. Johnson explains in detail in his most recently book, The Fat Switch, that overturn current concepts:
- Large portions of food and too little exercise are NOT solely responsible for why you are gaining weight
- Metabolic Syndrome is actually a healthy adaptive condition that animals undergo to store fat to help them survive periods of famine. The problems is most all of us are always feasting and never undergo fasting. Our bodies have not adapted to this yet and as a result, this beneficial switch actually causes damage to contemporary man
- Uric acid is increased by specific foods and causally contributes to obesity and insulin resistance
- Fructose-containing sugars cause obesity not by calories but by turning on the fat switch
- Effective treatment of obesity requires turning off your fat switch and improving the function of your cells’ mitochondria
I highly recommend picking up a copy of this book, which is a useful tool for those struggling with their weight. Dietary sugar, and fructose in particular, is a significant “tripper of your fat switch,” so understanding how sugars of all kinds affect your weight and health is imperative.
Study: Midnight Snacks Can Mess You up on a Molecular Level
I have long advocated that avoiding all food for at least three hours before you go to bed is an exceedingly helpful strategy for those seeking to maintain a healthy weight. This will lower your blood sugar during sleep and help minimize damage from too much sugar floating around. Additionally, It will jump start the glycogen depletion process so you can shift to fat burning mode.
A recent study9 is a powerful confirmation of this recommendation as it has found that the mere act of altering your typical eating habits — such as getting up in the middle of the night for a snack — causes a certain protein to desynchronize your internal food clock, which can throw you off kilter and set a vicious cycle in motion. As reported by The Atlantic:10
“Along with the usual slew of eating-related disorders, like obesity and diabetes, the researchers believe that this molecular understanding for why changing our eating times messes up our food clock might allow them to come up with novel treatments for conditions such as ‘midnight hunger,’ and to make better recommendations for people suffering the consequences of jet lag or working the night shift.”
Your internal body clock, also known as your circadian rhythm, helps regulate the energy levels in your cells, and the proteins involved with your metabolism are intrinsically linked to your circadian rhythms. There’s strong evidence that proper sleep and diet can help maintain or rebuild the balance between your circadian clock and your metabolism, and that lack of rest or disruption of normal sleep patterns can increase hunger, leading to obesity-related illnesses and accelerated aging.
In terms of its effect on your metabolism and weight, lack of sleep has been shown to affect levels of leptin and ghrelin—two of the hormones linked with appetite and eating behavior. When you are sleep deprived, your body decreases production of leptin, the hormone that tells your brain there is no need for more food, while increasing levels of ghrelin, a hormone that triggers hunger. (These are the same hormones detrimentally affected by a high-fructose diet, as discussed above.)
To keep your circadian clock functioning properly, make sure you’re getting the necessary amount of high quality sleep, during those hours when your body expects to be sleeping. The right amount for you is based on your individual sleep requirements and not on a one-size-fits-all prescribed number of hours. For helpful guidance on how to improve your sleep, please review my 33 Secrets to a Good Night’s Sleep.
The Case for Intermittent Fasting to Optimize Your Circadian Clock
In addition to that, this study offers an indication of how important it is to also maintain a regular eating schedule. Personally, I believe there is good reason to consider an intermittent fasting schedule. There is an emerging consensus that narrowing the window of time that you consume food may have enormous health benefits and also help you reduce your percentage of body fat.
Your suprachiasmatic nucleus (SCN), located in your hypothalamus, controls your circadian rhythms. It regulates how your autonomic nervous system operates along with your hormones, your wake and sleep pattern, your feeding behavior, and your capacity to digest food, assimilate nutrients, and eliminate toxins.
If you routinely disregard your innate clock – working during sleeping hours, or feeding at the wrong time – you will sooner or later suffer the consequences with symptoms that may include disrupted sleep, agitation, digestive disorders, constipation, chronic fatigue, chronic cravings for sweets and carbs, fat gain, and lower resistance to stress. Chronic disruptions in circadian rhythms have also been linked with increased risk for chronic inflammatory disease and cancer.
As explained by fitness expert Ori Hofmekler, the ideal time to eat is in the evening. Having a large meal during the day will inhibit your sympathetic nervous system (SNS) and instead turn on the parasympathetic nervous system (PSNS), which will make you sleepy and fatigued rather than alert and active. And, instead of spending energy and burning fat during the day, you’ll store energy and gain fat.
The one meal per day plan can accommodate your innate clock and maximize the beneficial effects you get from intermittent fasting on a daily basis. This form of intermittent fasting involves timing your once-daily meal to within a narrow window of time in the evening. However, you don’t have to be that strict if you can’t function without a mid-day meal. I’ve revised my own eating schedule to eliminate breakfast and restrict the time I eat food to a period of about six to seven hours each day, which is typically from noon to 6 or 7 pm. This still gives me a net fasting time of 17-18 hours a day. To learn more, please see my previous article, The Power of Intermittent Fasting.